Here's my NEWSWEEK colleague Sarah Kliff with an intriguing report from the Philly 'burbs, post-primary. Her basic thesis: that many of the much-discussed 164,025 Pennsylvanians who switched registrations from Republican to Democrat in recent months were already Democrats in everything but name, and were jumping ship only because they finally had an incentive--the first competitive primary in decades. This may be one reason why Obama didn't do as well as expected in the area. Pundits predicted that the switchers were primarily moderates under the spell of a "post-partisan"Obama. But it could be that many were already, you know, average Democrats--and thus as likely to pick the senator from New York as her rival from Illinois.

DELAWARE COUNTY, Penn.--"I hate to say this, but I think you, or maybe it's the punditry, but definitely the media, has got this dead wrong."

That's what Arthur Hirsch, a Bryn Mawr, Penn. resident, tells me when I ask him about his recent registration switch from Republican to Democrat. Hirsch is a nice guy, but he's frustrated with how the media has been characterizing him and 164,025 other Pennsylvania voters who switched their registration from Republican to Democrat prior to the Tuesday primary.

The Republican defectors, particularly the high numbers coming from the Philadelphia suburbs, have been described as a "tidal wave" who "just flipped from red to blue" that may "dim Republican John McCain's hopes of competing there in the fall."

The thing is, Hirsch doesn't see himself as much of a defector. And he definitely does not think he's dimming McCain's hopes at all: he has been voting for Democratic candidates for decades. "They think its because we've just become so enamored with the Democrats that we changed party," he says. "But there's a lot of us who are Republicans here who normally vote Democratic all along.

Pollsters with their finger on the pulse of Philadelphia's suburbs estimate that there are a significant number of voters out there who fit the Hirsh demographic: registered Republicans who regularly cast ballots for Democrats in national or statewide races. "It seems very logical to me that, in the Philadelphia suburbs, you had a good number of folks who have been voting Democrat for a long time and just now formalized it," says G. Terry Madonna, director of the Franklin & Marshall College Poll. "Before this, there was no reason. They could be registered Republicans, they could hate Bush and they could still vote against him in the fall." Chances are these Democrats in Republicans' clothes are not the majority--many such voters are indeed "Republicans who got excited about this primary or a certain candidate"--but Madonna estimates that this is a "significant category of voters that the media has largely overlooked."

Why the disconnect between voter registration and electoral behavior? Madonna and crossover voters give the same explanation: the closed Pennsylvania primaries. Because the Philadelphia suburbs are historically Republican-heavy, most of the competitive, local primaries happen on the red side of politics. Since the primaries are closed, voters need to register GOP to participate. "The closed primary makes you keep your party registration a lot longer than open primary states," Madonna explains. "Particularly if you live in a Republican area, Democrats would have trouble finding candidates." And access to Republican primaries doesn't cost voters anything in general elections-they can support either candidate.  So his take on it is that many suburban Philadelphians have kept their Republican registration, for access to heated local primaries, and voted Democrat in national elections. But in 2008, they finally had a reason to switch: access to a heated primary on the other side of the aisle.

Take Hirsch. He's from an area called the Main Line--the string of affluent, historically Republican suburbs west of Philadelphia. "If you want to have a say in politics, in things like the school board elections, for example, you have to register Republican" to participate in the primaries," says Hirsh. "When there is a race or competition, it's on the Republican side." So many voters who regularly vote Democrat in the presidential election--Hirsch included--register Republican to be able to participate in closed primaries for local politics. This year was the first when there was a competitive Democratic primary that he found compelling enough to switch his registration and support Hillary Clinton's candidacy.

There are no numbers or exit polls that get at the prior voting habits of the newly converted Democrats, so it's difficult to know how many have similar stories to Hirsch. But Madonna points to the counties' prior voting habits as one round about way to make an estimate. In the three big suburban counties surrounding Philadelphia-Montgomery, Bucks and Delaware-Republicans have held the majority of registrations for as long as any resident can remember, a fact pointed out in stories here. But Democratic presidential candidates have consistently carried the three counties since 1992. In Delaware County, where Hirsh lives, Kerry took 57 percent of the vote in 2004, and Gore took 54 percent in 2000--both at times when registered Republicans have outnumbered Democrats. So Madonna thinks its fair to estimate that "you have a large number of people who are registered Republican, act as Democrats and are just formalizing what they've been doing in practice."

Richard Kupersmith, a lawyer also from Bryn Mawr, is another voter who falls into that category. Kupersmith does have a few Republican skeletons in his closet--he was president of the Young Republicans club at his high school--but has consistently voted for Democratic presidential candidates since 1992. He and his wife, Susan, switched their registration five days before the March 24 deadline. "Up until this year there was not a Democratic primary where I felt like I needed to have a say in the outcome," says Kupersmith. "But this year, I want to say I had the opportunity to be involved and took advantage of that." He supports Hillary but will vote for whichever Democratic candidate takes the nomination.

According to voters like Hirsh and Kupersmith, this "tidal wave" of registrations may not make a particularly huge impact on how the Philadelphia suburbs vote come November. "It's a safe assumption to say that many of these were already Democrats," says Madonna. Which mean that in the general election "the Democrats may not pick up as many suburban votes as they think because they already had them."